What causes milky white cloudy aquarium water?

Guppies in the aquarium

Milky white cloudy aquarium water is often just temporary. Poorly rinsed gravel in a new aquarium can cause white cloudiness. Restarting the filters after a shutdown can cause debris and tiny air bubbles to create a white haze. Adding supplements such as bacteria, pH adjusters, or calcium can also create a temporary milky white haze in the water.

All of these sources of white cloudiness are usually just temporary, lasting only a few hours to a few days.

If the cloudiness persists, it is likely caused by bacteria growing at rates that turn the aquarium water milky white. This kind of fast bacteria growth is usually the result of excessive organic waste within the fish tank.

Causes for milky white aquarium water:

  • The aquarium is new and bacteria are settling. These nitrifying bacteria are needed as they make the water safe for fish by converting highly toxic ammonia to the less toxic nitrate (see ‘The Nitrogen Cycle‘ for more info). During the initial stages of a new aquarium setup bacteria and waste levels will not be balanced, often resulting in milky white cloudy aquarium water.
  • The bacteria colony has been disturbed by environmental changes i.e pH or temperature fluctuations or by anti-bacterial medication. Re-establishing of the colonies can cause the water to turn white.
  • Larger additions of fish or livestock can cause bacterial colonies to multiply every 20 minutes in an effort to convert the additional organic waste being produced. The re-balancing of the biological balance will require some time. Again the result can be milky white cloudiness.

With growing bacteria in the aquarium, oxygen can be depleted. To solve the problem, correct any of the above mentioned causes. Most common are the addition of livestock which causes dangerous spikes on organic waste.

Algone will clear and prevent cloudy water by removing organic and inorganic waste. Algone will also minimize ammonia and nitrite spikes and lessen their highly toxic effect on fish and other livestock.

Clear cloudy aquarium water, remove nitrates and simplify aquarium maintenance

Check out Algone here

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30 thoughts on “What causes milky white cloudy aquarium water?

  1. Lucy says:

    Hello! I wonder if you could help me. On Saturday I set up my Aqua first time fishkeeper tank. I cleaned out the tank, the gravel, and the plant I have in there. However in the package, there was no pump. I phoned up the shop and asked if we could still put the water in as it has to be in there 7 days before I add any fish and they said its fine to put the water in. That day the water started to get dark and cloudy but I just assumed it was because there was no pump to filter the water. I got my pump yesterday and got it all working but it’s gotten worse. It’s gotten even more cloudy. I’ve been adding in the conditioner and the bio boost as recommended yet it’s still very cloudy. I’m not sure what to do. I am planning on getting my fish between Friday – Monday but I’m not sure if I have to re fill my tank see if that helps due to the fact I had no pump to begin with or keep that water and hope for the best. Please help me.

    • Thilo
      Thilo says:

      The discoloration could be due to unwashed gravel or the plant soil. Starting over would be best in this case. Just drain the water rinse out the gravel and re-fill. I would not recommend the plant, there are substrate and light conditions to be met for the plant to thrive. Keep it for later once you got more comfortable with the aquarium.

      I would strongly recommend that you familiarize yourself with the cycle (link below). This is an essential part in setting up an aquarium. Keep things simple and always follow through with maintenance.


  2. Melanie says:


    We just started a new tank yesterday. No fish are added yet but we do have a couple of java ferns.

    I rinsed out the tank, the gravel, rinsed all the filter parts. Used aquarium conditioner, some bacterial supplement and some formula called easy care which says it balances chemistry, pH and alkalinity.

    We have added no fish or food or anything else. The filter has been running for almost 24 hours now. The tank is very milky/cloudy. The lights are a warm colour, so it looks yellowish.

    Any ideas of what to do?

    • Thilo
      Thilo says:

      Bacterial supplements can, and in your case did, cause a whitish discoloration of the water. Do keep in mind that your water chemistry will change once you add life to the aquarium. Right now, you are testing and treating tap water. My recommendation would be to familiarize yourself with cycling of an aquarium. This will help you a great deal in successfully setting up and maintaining an aquarium.

  3. Martin Novak says:

    I have identical five gallon tanks that I’ve run for nearly ten years. I say they are identical, because the contents are the same for both, as is the filtration. Recently, one tank has developed a tendency to a milky bacterial bloom each time I feed. Chemical testing shows 0 ppm for both ammonia and nitrites, and 30 ppm for nitrates. The fish are hardly overcrowded: until today, the tank housed a single neon tetra and a catfish. I feed once daily and minimize the amount of food. Both tanks are filtered with three-stage AquaClear filters and follow a regular maintenance schedule. (I’m so anal that I maintain a spreadsheet to track maintenance. Everything is the same for both tanks, yet one tank is crystal clear, and the other is perpetually cloudy. I’m out of ideas. Do you have any?

    • Thilo
      Thilo says:

      No two aquariums are alike, you can get close, but that will be as good as it gets.

      There are multiple biological and chemical reactions that make up the environment. These changes might be subtle but widen in the long run. Some affects are not immediate and will present themselves when they are least expected. There are many factors including even the fish behavior. Digestive system, some eat more some less which can cause more or less of one substance to be created. Everything triggers something.
      We have info on cloudy tanks readily available on our site, and it will provide you with the remedies you need.

  4. Jenn says:

    Put my new filter on in September was ok until , needed changing , started with bubbles and noise. The hob filter was sitting both for month , then just restarted both of them knew needed then, new one only giving me issues .

  5. Jerry Brown says:

    I set up my aquarium about 1 month ago. I put the water in with just filters for about 2 weeks. Then I added cycles and fish. It has been about 4 weeks now and I still have a slightly cloudy tank but I am now losing fish left and right. I have tested my water along with 3 independent dealers and ALL shows safe water levels. I added a canister filter thinking not enough filtration but no luck. I am running 2 Penguin 400’s along with a Marineland C530 canister filter. I have lost Angel fish, Tetras, Bala Sharks, and Iridescent Sharks. Any ideas are greatly appreciated. I really don’t wanna lose my entire tank. Everything I added fish I added stress coat. I also added a little aquarium salt per the dealers to try.

    • Thilo
      Thilo says:

      If all the water parameters are within acceptable limits, the next step would be to check on any signs of disease. Check the bodies of the fish, observe them to see if they are acting strange or unusual. Eating habits, any outside signs such as ulcers, inflamed gills, check the skin, fins eyes, and so on.

    • Chris says:

      If you haven’t figured out the problem by now all the fish may be gone but I have just stumbled over this thread and wanted to add something requarding the aquarium salt, I’m not sure if the problems started before or after adding salt or if you use it regularly and have been adding more when the dealer said to? That might be the problem of loosing your fish is to much salt in the aquarium for a freshwater setup. Salt doesn’t evaporate. Only way for salt to be removed is several water changes. I’ve read that another person was told the same as you and was using salt as recommended regularly. But she took the wording from the LFS the wrong way and was adding a small amount of salt daily as a remedy but having that much salt killed of the rest of her fish.

  6. Diane says:

    so Sunday (it’s now Tuesday) I walked into my living room and my 3 yr old niece was by my 10 gallon fish tank. It was extremely cloudy (greenish). She said she fed them and I believe it was a couple table spoons and shes pretty good about ratting on herself so I do not think anything else was added. But in the case that there was something else added I took all the fish out and moved them to another 10 gallon tank. Deep cleaned all gravel, heater, decor, air stone, filter, and changed the filter cartridge. I placed everything into new tank with fish. Gravel I waited until Monday after making sure it was very clean. I now have somewhat white, smokey, cloudy water. Water levels are all good.. So whats the deal?? HELP

    • Scott @ Algone
      Scott @ Algone says:

      Hello! When you basically did a whole tank cleaning you disturbed the nitrifying/beneficial bacteria which are needed for the healthy biological balance of your aquarium. The white water is likely a bacterial bloom which should clear up on its own as the tank comes back into balance. Your aquarium is probably re-establishing the nitrogen cycle.

      Just feed the fish minimally and avoid changing more then 10 – 15% of the water at a time. If the white cloudiness persist you can also use Algone to clear it up.

      • Scott @ Algone
        Scott @ Algone says:

        If the filter is running as it should, the tank will likely clear up on its own shortly. Likely you are experiencing a bacterial bloom which is quite common during the break-in of a new fish tank. Please be sure not to feed your fish too much food. Sparingly, once a day should help balance the tank. Too much food is the number 1 source of pollution and waste in the aquarium. Also avoid performing large water changes in hopes of solving the cloudy water issue. This will further disturb the balance of the tank resulting in a delay of the break-in.

  7. Luke says:

    Hi my Name is Luke and this is the second five gallon aquarium I have had. I have A Fluval chi and one betta. i have been through alot. So please Stay with Me… When I bought The tank I had a betta and an african dwarf frog. And then i got a neon tetra the water never went throught this cloudy stuff at the begging. then algea started growing on the inside of the tank so bieng dumb but reading online they said water changes and a sponge also the gravel was dirty. Anyway I did a 100% water change and killed my neon tetra and my adf died of a disease few days before. Then I got a dwarf gourami and a algea eater (i know major overstock) so The next day i gave both those fish away and got a guppy(wich suprisingly got along with my betta) and then I did a gravel vacuum 75% water change and killed the guppy. So know i have one betta. Know the cloudy Water is back and I tried api accuclear which says clears water instantly but 12hrs later water got cloudier. so i will re apli, what do i do. And the weird thing is i was 7 when i had my first 5 gal fish tank and it never got cloudy. Please help.

    • Thilo @ Algone
      Thilo @ Algone says:

      Small aquariums can be more tricky than larger ones. The whitish water indicates a bacteria bloom. Bacteria use up oxygen. Before and during the bloom, you might experience higher elevations of ammonia/ nitrite.

      Changing 75 – 100% of the water dramatically changes the environment of the fish. That includes pH levels and other vital parameters. You should never do such a large water change. Excessive cleaning can decimate the bacteria colonies.

      In your case, cloudy water indicates that the bacteria colonies are repopulating, growing at rates that turns the water cloudy. For the benefit of the bacteria, you should be patient and leave the cycling of the aquarium as nature intended without interference at this point. Monitor the aquarium for ammonia/ nitrite/ nitrate. Once the first two values read out at 0 ppm, and nitrates are detectable, the cycle is complete and you can start with corrective measures if needed.

  8. FishAddict says:

    Ok so, my tests came out where it is supposed to be just right for my mollies. I do not have overstock unless ssomene lied to me about how many gallons my free fish tank is… I did measure it with my measuring tape app.
    My tests always come put right.
    This couldnt be true.. Except i have been pufting in warm water for my cold aquarium. And i have a heater. So everytime i have a cloudy tank my fish cannot breathe. Its the second time too. Blah

    • Thilo @ Algone
      Thilo @ Algone says:

      Cloudy milky water is a bacteria bloom, and bacteria need oxygen. In severe cases of cloudiness oxygen can get depleted to the point where it becomes dangerous for the fish. In any case, if you can provide sufficient oxygen to the water by means of the filter, the fish will be just fine. Take it as a precaution.

      Bacteria blooms often occur with the water parameters quite in range. Reasons include overfeeding, using water conditioners with added bacteria, high biological load (plants, fish and other organisms) lack of maintenance (cleaning the gravel) medication, and sometimes it just happens if the bacteria are disturbed.

  9. maryjane mckenrick says:

    Please help, I cannot clear the water in my saltwater tank, andbut I don’t want to quit!!!I am losing all my fish, I have tried everything I’ve read…PLEASE HELP I don’t want to lose them all…aND it’s costing me a fortune…b

    • Scott @ Algone
      Scott @ Algone says:

      So sorry to hear you are experiencing fish loss. I assume the aquarium is newly setup? If this is the case you should read about ‘new tank syndrome‘. Cloudy water itself is rarely a threat to fish life. It’s the underlying nutrients that spike that can become lethal.

      You should test your water for ammonia and nitrite. Both precede the more commonly known nitrate and are the result of waste breaking down in the aquarium. Ammonia and nitrite are quite lethal if fish are exposed to them for prolonged periods. They inflame the fish’s gills and make it difficult for them to breath.

      If either ammonia or nitrite are present in the water, I would recommend cutting back on feeding to once every other day. And sparingly at that. This will be a temporary situation and your fish will not starve due to this. The idea is to limit new waste entering the fish tank. Waste eventually breaks down into these problem nutrients. 10 – 15% water changes every 3 – 4 days should also help bring down these toxic nutrients. A well balanced tank will only have detectable nitrate, but never ammonia or nitrite. Beneficial bacteria aka nitrifying bacteria need to establish in sufficient amounts in the tank to successfully break down waste into the less toxic nitrate. This bacteria is usually lacking in new aquariums or tanks that have gone through significant changes. Introducing several new fish, large water changes, a breakdown and complete cleaning of the aquarium, an overstocked or overfed fish tank, all can be the reason for a bacteria imbalance.

      Here are a few links with some info that may be helpful:

      Nitrifying Bacteria
      The Nitrogen Cycle
      Aquarium Ammonia
      Aquarium Nitrite

      Also check out Algone. It clear cloudy water AND removes excess nutrients from the aquarium.

  10. jamie says:

    What is the white build up on my fish tank i have not yet put any fish in due to it because it looks a bit like fine skin?how could I prevent this

    • Scott @ Algone
      Scott @ Algone says:

      It may be some fungus or mold buildup if it’s growing on the gravel and/or glass. This is usually not a threat to fish life but you should remove it just to be safe. Fungus/mold feed on organic waste in the tank. Even though there are no fish in your tank, the substrate may have contained sufficient organic matter to cause this.

      White cloudy water, as outlined in the article above generally indicates a bacterial bloom. Click here for tips on clearing cloudy aquarium water.

  11. Kip Jordy says:

    Virtually all pet stores have crystal clear water. How do they manage it?

    I have tested the water from PetSmart, PetLand, and WalMart. All three of them have 0 chlorine, 0 ammonia, a hardness of about 100, and a pH of about 8.4 (quite high). My tanks have a lot more ammonia and a lower pH (and my tanks are at best a bit hazy – never crystal clear).

    • Scott @ Algone
      Scott @ Algone says:

      Pet stores usually run all of their aquariums via a shared filtration system. This means they have a much larger water volume then meets the eye. The greater the volume of water, the easier it is to maintain as it is far more forgiving and more difficult to throw out of balance.

      As far as your tanks, you should never have detectable ammonia unless you just set up the aquarium. Ammonia inflames the gills of fish and makes it difficult for them to breath. It is quite lethal if fish are exposed to it for a prolonged period. Further, the pH should have no bearings on hazy water.

      You can use Algone to reduce ammonia, nitrite and nitrate. Algone also polishes the water crystal clear.

      Detectable ammonia in the aquarium indicates some type of imbalance with the nitrifying bacteria. This can be caused by accumulating waste in the tank (overfeeding), changing too much water too frequently, adding new fish, overstocking the tank, failure to keep up with maintenance. Basically anything that causes a dramatic change in the aquarium’s overall bio-load or causes tank conditions to deteriorate.

  12. ericB says:

    I recently bought a 150 gallon tank .off a friend and I decided to go with sand instead of gravel..I also bought a fake coral piece from petsmart I filled the tank up and it’s been setting a week and all the sudden it’s milky white ..I wanted to run it for a whole before I put any agressive stock in it ….CAN ANY ONE HELP WITH THIS NOT SURE WHAT TO DO ITS ALREADY SETUP

    • Scott @ Algone
      Scott @ Algone says:

      You are likely experiencing a bacterial bloom which is not uncommon after initial setup of an aquarium. Beneficial bacteria establish during the first weeks of a newly set up fish tank and white cloudiness can result due to an over abundance of this bacteria. In most cases this will clear up on its own as the tank balances. The only potential treat of a bacterial bloom is the (remote) possibility of de-oxygenation of the aquarium since the bacteria uses oxygen. For this to become a threat to fish is an extremely rare event and very unlikely to happen.

      It;s best to side on the side of caution however and test the water for ammonia and nitrite before interdicting fish. Both are lethal to fish if exposed to high levels over extended time. It is normal to have ammonia and nitrite spikes during the cycling of the fish tank. Once established (usually 4 – 6 weeks) both should be undetectable and only far less harmful nitrate should be measurable in small to moderate amounts.

  13. Thilo @ Algone
    Thilo @ Algone says:

    Cloudy water does not just have one single cause. It is a variety of excess waste that triggers the water to turn cloudy. Algone removes a variety of substances that will help clear the water, but it is the total amount of this waste that determines the time frame. In addition, it always helps to minimize the feeding and to consider supporting measures such as increased maintenance.

    Additives such as water conditioners containing bacteria, or anything similar, should be discontinued until the water clears back up again. Water changes should not exceed 10% per week.

    Lastly, and for the majority of the cases, the water clears up literally overnight. A gradual or visible improvement is rarely observed. Once the excess waste is below a certain threshold, the water clears.

  14. Joy says:

    Hi. I have a question. I did use algone for two weeks now but cloudy water of my fish tank is still there. It’s like nothing happen. Please help me